1. Field of the Invention
The present invention relates in general to a windshield wiper, and more particularly to an electric motor assembly for the windshield wiper, which includes a motor part and a speed reduction gear part combined as a unit.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional electric motor assembly for the wiper will be described with reference to FIG. 4 of the accompanying drawings.
Referring to the drawing, there is shown the conventional wiper motor assembly 100 including an electric motor part 101 and a speed reduction gear part 102 which are combined as a unit.
The motor part 101 comprises a motor housing 103 in which known motor parts are housed. A driving shaft 105 of an armature (not shown) extends outward from the motor housing 103 into a housing 104 of the speed reduction gear part 102. The shaft 105 in the housing 104 is provided with both first and second worms 105a and 105b which are spiralled in opposed directions. First and second identical compound gear members 106 and 107, each including a larger diameter helical gear 106a or 107a and a smaller diameter gear 106b or 107b, are rotatably arranged in the housing 104 at opposite positions with respect to the driving shaft 105. As shown, the helical gears 106a and 107a of the compound gear members 106 and 107 are meshed with the first and second worms 105a and 105b, respectively. It is thus to be noted that rotation of the driving shaft 105 in a certain direction rotates the first and second compound gear members 106 and 107 in the same direction at the same speed. A bearing structure 109 is further arranged in the housing 104 for bearing an output shaft 108 of the speed reduction gear part 102. An output or terminal gear 110 is secured to the output shaft 108 to rotate therewith and meshed with both the smaller diameter gears 106b and 107b. Although not shown in the drawing, the lower end of the output shaft 108 is projected outward from the housing 104 and connected through a known pivot-motion mechanism to wiper blade assemblies.
Thus, when the driving shaft 105 rotates due to energization of the motor 101, the output shaft 108 rotates in a given direction, thereby pivotally reciprocating the wiper blade assemblies to wipe an associated windshield.
However, due to its inherent construction, the above-mentioned conventional wiper motor assembly 100 has the following drawbacks.
That is, in winter, when the wiper blades have frozen to the windshield or a considerable amount of snow has laid on the wiper blades, energization of the electric motor 101 causes generation of great load or stress on the meshed parts of the speed reduction gear part 102. Under this condition, the teeth of the gears tend to break and in the worst case, the motor 101 breaks.